Originally Posted by spyderjon
Atomicman, for some reason I can't open the Holmenkol tech pages, either from your links or via their website so I can't gen up on backfiling.
I understand how one would backfile & I've used a sidewall planer but could you explain why/when one method would be chosen over the other?
My reckoning is that backfiling is removing metal from the 'top edge' of the actual side edge as opposed to the skis sidewall material?
this is the original article I discovered backfiling from: Oops wrong article let me look again!
here it is!
Ski Racing – Issue #1 – The Buyer’s Guide Back Shop
You’ve asked around, checked out what your favorite World Cup athlete is on, tested at Mt Hood, maybe even scored some special “secret” version of the skis you know will help to put you on the podium this winter – but wait – you’re far from done. Even the best skis don’t have a prayer of performing unless you put into them what you expect out of them – and that means a great prep to get the season started off right. There’s no better time than now to get your personal plan together for finding and creating as much speed as possible, both in yourself and in your equipment.
In the front half of this issue, our first of the new season, you will read about all the hot new skis, boots, bindings, and gear that are specific to alpine racing. And, if history holds true, you will shortly be the proud new owner of quite a bit of that high tech racing gear.
So, from A to Z, here is your complete guide to the when to, how to, and why to of new ski prep:
Step 1 – unwrap & examine. Do this yourself or with help of a trusting coach or technician. Place the skis together tail down on a firm surface, and close them at the mid point (where the middle of your boot would be). Now look closely at how the ski closes. Note any large gaps that may exist – it’s not a sign of a bad ski, but rather, of the ski continuing to cure (it takes about 90 days for a ski to cure after coming out of a mold). Large gaps can be worked out using a bending bar in the hands of a knowledgeable ski tech. Small gaps won’t matter and should be ignored. Next, put your skis in the vise base up, and scrape the factory wax off completely. A few quick swipes with your brass brush will expose the factory structure. Now, begin to carefully check the flatness of the base material at about 8 to 10 points along the length of the ski. You are looking for a base that is consistent along its length, neither high nor low as compared to the edges. The edge will most likely be slightly below the plastic base. Base material should be free of waves and without noticeable “hair” from the grinding process. If the base is not flat, you will need to stone grind right away. If it is flat, you will need to decide if the factory structure is appropriate for you. In most cases, the factory structure will be appropriate – today’s race room skis are closer in their development cycle to World Cup skis than ever before. Again, careful consultation with your race rep, a trusted coach or technician will guide you here. If in fact you are grinding new skis, decide if you need to completely remove the existing structure or simply “knock it down.” Many race skis can be flattened to near perfection with just 6-12 extremely light passes over a nearly structure free stone, resulting in an effect much like “mowing the lawn” – the structure’s depth is lessened, but not removed, and the ski is rendered flat. In instances where new skis need to be flattened, this is often the best approach to take, because it retains the proven factory grind yet allows the technician to work out the high & low spots that have popped up since it left the factory.
Step 2 – base work. Now is the time to try to “break in” your bases. There are many anecdotal methods of doing this; basically, you are trying to smooth out the micro-structure of the base. This approximates the wear and tear that will occur from the snow crystals – but of course your effort is more even along & across the base. You will need a range of tools – a stiff steel brush, regular steel brush, stiff brass brush, Scotchbrite® pads, and sandpaper (320 or 400 grit wet/dry type aluminum oxide sandpaper). The overall goal is to get the base working for you by making every edge of the micro-structure smooth, not jagged (you are not trying to erase the structure, just make it faster). The brushes will work the bottom of the structure, the sandpaper the top of the structure, and the Scotchbrite® pads a little bit of both. Always work from tip to tail, and keep track of how much work you put into each step so you can repeat it on the other ski! Unfortunately, there is not a specific formula to follow here. The best bet is to understand the goal, and work towards meeting it, rather than just blindly banging away on your bases. I like to really look at the structure up close and create plan of attack. If I am trying to accentuate the existing structure, I may start off with a stiff steel brush (BBQ brush). If I am trying to smooth out a structure that has tall peaks (record grooves), I will start with sandpaper wrapped tightly around my true bar, working in long smooth strokes from tip to tail. I always brush with a regular steel brush, then stiff brass, then Scotchbrite®. Those three items should take at least 20-30 minutes per pair. When you are done, perform a good hot scrape cleaning to remove the factory gunk and your own dirt. How to perform a hot scrape cleaning? Easy – start with about 100g of inexpensive, warm temp (non-fluor) wax. Wax your skis with this wax as you normally would (plenty of wax, allow the skis to become warm and reverse camber, keep the iron moving smoothly from tip to tail); when the wax is liquid from the tip to tail, scrape quickly with a sharp scraper. Keep scraping until you can pull no more wax out; re-wax (no need to let the ski cool) and scrape again while liquid. Keep hot scrape cleaning until the wax comes out without any dirt / debris in it!
Step 3 – base edge. At this point on a new ski prep, I prefer to completely tape off the plastic base using ski tape. I do this because the next several steps are bound to create a mess, and I prefer not to grind that into the clean base that I have created so far. Start by finding the widest part of the ski at the tip & tail – they may likely be well past the contact point – and round the edge over from the base towards the sidewall BEYOND the widest point using a mid sized file. Now examine your tail cap – if it is metal, round it over as well; if it is plastic, you can round it as well, but will need to sand the plastic tail cap smooth when you are done. Next, determine your desired base edge bevel (volumes have been written on what degree to use; consult Issue #___ of last season’s Ski Racing, your coach, and your technician). Many North American technicians I know prefer to use the same degree the whole length of the ski; however, most European techs I know prefer to vary the degree, using more base bevel at the tip (10-15 cms) and tail (5-10cms), with a consistent bevel in the middle 80% of the ski. The difference? Subtle. All things being equal (and they never are…), the ski with the same base bevel along its length will hookup more quickly a the start of the turn as the ski is tipped on its side, engaging the complete shape all at once. The ski with slightly more base bevel at the tip and tail (side bevel is always the same) will engage the entire shape more progressively. Go with what you feel comfortable doing. Your choice of base beveling tools is highly personal, but be sure you are comfortable with it. Anything from a precisely folded cloth to various incarnations of shimmed guides will work – again, it is your feeling for the tool, your control, and not over-doing that will most positively effect good results. Always use your sharpest, finest file (be sure to check it for flatness before using it!). It only takes a few passes to set the bevel – avoid the trap of over beveling, leaning on the file to get it to keep cutting, and bending the file. I like to use the two thumbs approach – I press the file straight down with both thumbs, with my left thumb over the center of the base and my right thumb directly over the edge, while pulling back smoothly. When you are done, you can polish the base edge buy holding a gummi block directly over the base edge, applying strong pressure, and working the gummi block back and forth.
Step 4 – Side Edge at tip & tail – Now, turn your ski on its side in the vise. Find the spot PAST the widest point (remember, the widest point may well be very different than the contact point – the ski works from the widest point to the widest point, even if it doesn’t appear to touch the snow) at the tip & tail that you previously rounded over from the base side; now, round that area over again from this side. At this point, this part of the ski (which does not contact the snow) should be completely smooth and rounded. Use your sandpaper (320 grit) to finish this area off, polish lightly with a gummi.
Step 5 – sidewall prep – owners of monocoque skis can skip ahead to step 6 here….The purpose of sidewall prep is allow the ski to slice thru the snow, to allow the technician to gain reliable, consistent access to the side edge for tuning, and to finish off the factories production effort. Take a look at the 4 options you have and decide which is best for you & your skis (see graphic) Start by severely rounding off the junction of the sidewall where it meets the top sheet. You will need a new, full length cross (panzer) file for this operation, as well as some sandpaper. Pay attention to the skis construction – does it have a metal top sheet under the cosmetic or not? You can be more aggressive if you have a metal top sheet than if you do not. Take a good look at the tip and tail sections that do not contact the snow, and be sure they are completely rounded, too. If you have a pile of material at your feet when you are done this step, you are on the right track!
Step 6 – sidewall prep – edge area. Next, we will focus our attention on the small lip that sits directly above the steel edge. This lip is composed of sidewall material, and also likely to be composed of some layers of glass and rubber. Examine it closely to see its construction, and if there appears to be a “2nd edge” above the steel edge – most likely there is. Your goal here is to angle or radius this material. Start by using either an SKS tool, or a sidewall planer than can tackle the aluminum layer and the other material. Pull in long, smooth strokes, being careful not to create “chunking” at this point. Success here is crucial – take your time, and be sure your tools are fresh and up to the task. Keep going here until it is noticeable that the edge is sitting out on it’s own, but not so much that there is no support structure above it at all. Monocoque ski owners will also have good luck with aggressive sandpaper wrapped around an old scraper, and held at a 45 degree angle to the side edge lip. This allows the edges support structure to be blended nicely back in to the skis sidewall structure without tearing into the structural cap of the ski.
Step 7 – the in between area – monocoque owners skip this step… Now that you have rounded the top edge, and radiused or angled the edge lip area, you are ready to tackle the sidewall in the middle of these two zones. The goal here is to remove enough to smoothly blend the two previous steps together, and to be sure that the angle of sidewall does not vary (use a true bar on the side to check; it should fall away towards the top sheet consistently, not towards the edge). Use a sidewall planer and sandpaper for this step. Blend extensively with sandpaper, working from 220
thru 600 grit; then finish with a rag soaked in acetone immediately followed by a Scotchbrite. Your sidewalls will be super smooth!
Step 8 – setting the side edge angle – Now, you are ready to dive in to the steel. Most folks are running a 3 degree side edge angle today for all skis; some younger racers (J6 thru J4) may also be running a 2 degree side, which is OK, too. I like to make 1 or 2 passes with a 5 to 7 degree angle using a cross (panzer) file along the whole length of the edge; this allows the top corner of the steel to blend nicely with the sidewall. Next, begin sharpening your side edges using the cross (panzer) file and 1 degree more than you intend to run – use a 4 degree if you intend to finish with a 3. When you have a sharp ski from tip to tail, move to a mid or small sized file with the final angle you want, and continue sharpening. The process of finishing the side edge is designed to continually smooth out the previous work, leaving you with a nice smooth, grippy edge. I like to make a few passes with a middle grit diamond file next, of course attached to the file guide. This will really soften the rough effect that the file has left. At this point in a new ski prep, I will take an Arkansas or ceramic stone and lightly pass it along the base edge to cut the “curl” of steel that has developed from all this filing. I usually do this freehand, with light to medium pressure. Now you are ready to really put the edge on – use your Arkansas or ceramic stone with your file guide, and begin working the side edge steel back and forth until it is extremely smooth and sharp. A light pass on the base edge side with your gummi block will finish the edge off, and you should have a very sharp, smooth edge that is ready to ski.
What is sharp? A few words on how best to check sharpness:
1. Pull your hand (back of palm, back of fingers, or the 1cm zone where your wrist meets your palm) lightly across the edge at an angle which is roughly flat to the sidewall. This will give you a sense of the sharpness. Many folks will pull at about a 45° angle to the edge; rental skis can feel sharp with this technique.
2. Using the end of the cuticle on your thumb, lightly pull it across the base edge from the p-tex towards the outer edge. If the edge pulls a small amount of nail off, this indicated that you have some degree of a “curl” left from your sharpening. It is most times best to polish this off, and then re-check that you are still actually sharp. Don’t confuse having a slight curl with being truly sharp.
3. Some professional service technicians will purposely leave a very slight curl on the base side for men’s events on injected snow, or if they are unsure just how hard the snow will be in the AM, this allows them to dial the tune back at the start before the athlete skis on the ski.
Step 9 – remove the tape from the base, begin to re-brush the skis from tip to tail. I like to use a brass brush for this. A quick pass with some fiberfleece will pull up any small bits of dirt, and you are ready to begin wax cycling. I also like to spray the top sheet of the skis at this time with an anti-stick product – most wax companies make an inexpensive Nordic product for no-wax skis that you spray on the “fish scales”, which works GREAT for the top sheets of your skis to keep them clean and free from wax debris. Much has been written about how to wax cycle your skis to make them fast; basically, you goal is to fill the bases up with as much wax as you can (softer is better to start with, then move to middle/harder waxes, always use hydrocarbon waxes for this, not fluor waxes) while you also help to break in the bases thru the repeated scraping and brushing that you will do between coats. Always let the wax cool and harden completely, best is 6-12 hours before scraping, brushing, and re-waxing. Repeat this as many times as you can – not less than 3 times – before even thinking about letting those skis hit the snow.
Step 10 – repeat for all the other skis in your quiver!